Adjusting the retrograde condensation pressure of hydrocarbon compositions



Patented Ocala', 1355.

Y v "z,1'zo,z`6s ADJUST- ING ran nErRooRAnE coNnENsArroN .PRESSURE or uYnRocAnBoN coMPosmoNs Jopll H. Tracht, Pittsburgh,l Pa., assgnor to Re search & Development Company, Pittsburgh, Pa., n oorpomtionofD'elaware j f v Application Massaal, 1954,'sen1 No. 420,153

i' invention 'relates `theu'rccover'y of liquid disoil` and gas wells, and has particular reference to a. method of treating the contentsV of high pressure hydrocarbonreservoirs soas to increase their total liquid yield.

' ,In certainhigh pressure' naturally occurring petroleum reservoirsnormally gaseous and normally liquid hydrocarbons exist in a single' phase usually termed a gas sgas-like'phase or be redissolued in the single phase. The

Vdissolved distillate iluids 'willconsequently be carried to tillate hydrocarbons at high pressures from high pressure phase. The pressures in the formations'of thse wells are-usually between about L200 and 10,000 pounds per l square inch and the temperatures are usually between about 130' and 300 F.

.Under normal conditions of temperature and pressure, the ratio oi Agas to liquid in a heterogeneous gas-liquid tion .pressure resulting from ny 'treatment of the well fluids will cause the distillate fluids to remain' in the single the producing surface and be recoverable `there. j

It is a well known practice to return gas by ineovtion-or input' well to the formation beyond that amount of'gas that it 'is permissible, to recover relative to the recovery of oil. The increased recovery of oil provided" by the method ofvthis invention decreases the amount of' gas that mustbe returned to the formation; on the other hand existing provision for returning the gas through the' input wells will provide some if not all. of the equipment necessary for the treatment of wells according to the'I method of this invention. According to this invention the hydrogen sulfide conf, centration of 'the' input gas is so adjusted that the hydro.

gen .sulfide will have a 'concentration in thatportion of the formation which it 'penetrates'of between -1 and 30 percent by volume. As demonstrated more specically' in the following description of the vmethod of inventions.` v the' optimum hydrogen sulde concentration of the Well" fluids is maintanedwithinthe said' liin'tstby 'several1 methods of adjusting the hydrogen sulde content of the' 'Y recycled gases or by direct addition of hydrogen sullde- .-from an' outside source. Separation in apparatus at the' surface of hydrogen sulfide-rich acid gases from'the produced lluids and the addition of predetermined quantities' mixture increases with increase in temperature and decrease in pressure, and conversely decreases with tcmpcrature decrease and pressure increase; However', at

' temperatures above the critical point,.which lie's on the of the said gases to recycled gases can also be' employed."

Depending upon thetemper-anire and concentration" Y of the liquid hydrocarbon mixture, the incipient retro grade condensation pressure can vary from .aboutiOOf phase envelope of the mixture, and below the critical condensation isotherm an apparent reversal of the expected change in phase is encountered, and a decrease in pressure will effect -a condensation of liquid from the gas..

The .phenomenon of forming a liquid condensate upon reducing rather' thanA increasing pressure isknown as retrograde condensationvorjmore precisely isothermalretrograde condensation with decrease in pressure (Volumetric and' lPhase Behavior of Hydrocarbons, Sage & Lacey; Appendix, p. 293) andthe rangewithin which liquid condenses from solution is known as the retrograde condensation range. The retrograde condensation temperature range of the lighter hydrocarbons is relatively high and occurs at temperatures between the critical temperature of the hydrocarbon mixture and the cricondentherm of that mixture.

While it has been the practice to exploit the retrograde condensation of liquid hydrocarbons in the recovery vof distillate hydrocarbons from well -uids by reducing the. pressure on the produced well lluids and separating the condensate, the phenomenonalso results in substantial loss in 'the reservoir of distillate hydrocarbons which condense as reservoirpressures decrease. i

Brielly stated, my invention comprehendsthe adjust `ment of the retrograde-'condensation pressure of petro vleuxn hydrocarbon uids at elevatedpressures by establishing a predetermined hydrogen sulfide content of said fluids, increased hydrogen sulde concentrations decreasingfthe retrograde condensation pressure and decreased concentrations increasing the said pressure.

pounds per square inchto the maximum pressures en countered irtdeepv well operations'. Specic conditions in any' particular well` will govern the amoung I of hydrogen sulfide which should be added to the formeq; tion or the optimum concentration of hydrogen sulfide thatf should be maintained in the `input gas. The operation- -of a Aprimary gasoil separator at the wellhead inusual;l

condensatefreservoir operation employs retrograde' con- A densation for primary separation of distillate -hydrocarjbons.- The optimum concentration of hydrogen suliidej v the purpose of illustrating and not -of limiting the invenfg'v to be maintained in the inputv gas can be determinedl with suicient accuracy to procure thedcsired results by observe' ing variations in the operating characteristics of the saidfY observations to con-0- gas-oil separator and adjusting these formtobottom-hole pressures. In-theaccompanyingdrawings which are supplied for tion,

. Fig. I is elevational flow-diagram of a plant for pro-I ducing liqueliable hydrocarbons from a condensate rea-Q of the underlying pro ervoir and a schematic diagram ducing formation, n

Fig. 2 .is an elevational ilow diagram of a systetntdr, the production -of well uids from a combination con-.g

' densate and crude oil reservoir,

More specically, my invention comprises a treatment v of fluids in the reservoir of gas condensate wells' by in jection oihydrogen sulfide, or of gas containing hydrogen' sulde, to raise the concentration of hydrogen sul# de in the reservoir an amount within the range of l to 30 percent by volume of the total well uids being treated, wherebythe retrograde condensation pressure of the hydrocarbon liquids constituting the well fluids is decreased. When depletion of the well results in a decrease in the Y formation pressure, the decrease in retrograde cndcnsa-V Fig. 3 isan elevational ow diagram showing recclwf'v 'ery operation from apartially depleted crude oil reset-' Fig. 4 is a curve showing-the etect of the hydrogenir;` sulfide concentration on the retrograde condensation pres-f can represent aplurality of separators ordinarily posed in series. The pressure in the gas oil separator; 13 is maintained below the retrograde condensation pres-`v sure and the temperature is reduced to a.temperature;0 y

With particular reference to Fig. l, producing gamonav v densate well 10 'isemployed to recover gas and oil'fom'- a high pressure formation 1 1; The well producesuidsgj.` under high pressure. which ow from the well 1 and' through avalved line 12 into a gas-oil separator 13- which f below reservoir temperature. Separated liquefied hydrocarbons are flowed from the separator 13.thro` ugh' valved "line 14 to storage or utilization means or the like (not 55 which -can represent also conventional means for sepa'- "ration, drying or compression of die acid gasesv shown). Gas-from the separator 13 flows from line 1S to the scrubber 16 in which the gas dows countercurnentlyl to a treating solution such as an aqueous solution of ethnnolamne. 'The amine treating .solution removes acidV gases 'from the gas and the so-enriched amine solution 1 flows from the scrubber'16. through a line 17 into re'- genmtor 18 in which heat is employed to strip the acid 'gases from the amine. Regenerated aminesolution is recycled from the regenerator 18 through line 19, and

Light petroleum gas substantially free of acid gases4 tlows tro'm line 50 vinto a liqueed-fpetroleum-gas plant 56 which yields product4 liquids or natural gasoline which j are-'withdrawn from line 57 to storage or utilintionmeans not-sitcom.` Dryorlean gas ilows from them.'

plant 56 through n valved line 58 and Vis mixed with# measured amount of hydrogen. sulde in acid gases owf i ing from storage means 55 through a valved line 59.

gases from which acid 4gases have been removed dowthrough line 20 into an absorber 21 for recovery of the" heavier hydrocarbons in the gaseous fraction. The gases enter absorber 21 and are scrubbed therein by an absorbent oil.' The oil, enriched l with absorbed hydrocarbons, flows through line' 22 into a still 23 wherein the absorbed hydrocarbons are stripped and passed through line 24 to storage or utilization means (not shown). Regenerated scrubber oil is recycled from'the still 23 absorber 21 ilows through line 26 to a compressor 2 7 acid gas and the l'ean'gas are-mixed in line 60 and 'are pumped 'by a pump 61 disposed therein into input well 62 which penetrates the gascap formation 63. Thus hydrogen' sulfide is added to the gas cap at the same time that gas is injected to maintain producing pressure and drogen suldewill have been added to the gas cap 1o significantly lower the dewpoint of its contents making through a line 25 to the absorber 21. Lean gas from the which raises the vpressure of the gas to -above the pres-i' sure lof the formation. Compressed' gas flows from the compressor 27 through lline 28 and is mixed vtherein with a measured amount of hydrogen sulfide introduced into the line 28 from the regenerator 18, line 29, compressor'- f 30,an diine31. The mixed recycled gas is introduced through valved.A

line V32 into the input well 33 vby which means the re'- cycled gastis introduced into the producing formation- 11. The hydrogen sulfide-rich recycle gas ows through the formation and'vtoward the producing well because of the induced pressure differential. Hydrogen sulfide from any other source can be introduced by the compressor 3B in measured amount into the formation.

Highly concentrated or pure hydrogen sulfide can intermittently be introduced into the formation 11 and thus pass'through the formation in relatively high concentrations even though diluted by the fluids in the formation. These surges of gas more concentrated in hydrogen sulde are introduced to provide'an even ,greater potential to redissolve condensed hydrocarbons in the ga'se.- ous phase. The' solvent power of the hydrogen sulfide-enriched cycled gases will redissolve oil which has condensed in the formationi by retrograde condensation as reservoir pressure decline;

A well producing c mdeoil under pressnremaintained -over the producing formation-by a gas cap in the reservoir is shown in Fig; 2 in which producing wellst40` penetrate the oil formation. In the example illustrated when all of the recoverable oil is produced suicient hythe production of the petroleum constituentsof the gu' cap more etiicient. As the hydrogen sulfide-rich gas 'is injectedinto the top of the reservoir and the final blow?" downzafter Voil production is accomplished through the' wells previously used for oil production, the hydrogen sulfide-rich gas' expanding behind the gas being producedwill automatically sweep up any liquid condensate leftmvbehind According to Vthe foregoing procedure, the

lowering of gas pressure in the formation during oil' production is reduced by the recycle of the lean gas and,

to the extent that'hydrogen sulfide that was separated' from the well fluids is ladded to the formation, the retrograde condensation pressure of the gas in the formation' will also be lowered; Where it 'is desired to reduce still further the gradual decrease of gas pressure in the forma-1 tion, 'which occurs as crude oil is being produced, or to 1 maintain a fixed pressure, lean gas from an outsidef source can be added to the cycled gas. In like'man-x ner hydrogen suliide from an outside source ,can be added to the cycled gas, whether or not lean gasA l' from an outside source is added, in otder'to itt-1 'increase1 the hydrogen sulde concentration of the by Fig. 2 oil is owed from the'producing wells 4Q through valved lines 42 and 43 and line 44 into gas-oil separator 45 which can represent several separators usually arranged in series and which is operated at a pressure below'the reservoir pressure. Liquetied hydrocarbons are with` drawn from the separator 45 through line 46` and are passed into a stock tank 47 or other means (not shown) for refining, utilization or storage of these liquid hydrocarbons. Gas is flowed from the gas-oil separator 45 5.5. 4is pressured upon substantial depletion of the oil pr'o" v duction to a pressure in the retrograde condensation range v and which is subsequently operated as `a combination crude-oil and'gas-condensate-well. During crude oilpro-y through line 48 into @absorber-49 of an amine treating i plant. G'asjrom which acid gases, particularly hydrogen sulde and carbon dioxide, have been removed is flowed from the absorber 49through a line 50. The amine treat ing4 liquor, which can for example be a solution of ethanolamine, and will contain hydrogen sulde and other acid gases, is removed from the absorber 49 through line v 51 and is owed therefrom into a regenerator 52 in which.

heat such las steamv s employed to drive the acid gases from the amine treatingsolutionthereby regenerating the solution. The regenerated solution is returned to the absorber 49 through the line 53. Acid gases which are stripped from the amine treating solution in the regcnerator 52 flow thrr ugh valvgi line 54 into s storage means gas in the formation and thus, according to the; present invention,4 lower the retrograde condensation; pressure and ensure increasedyields of liquid hydrocab' bons during subsequent condensate-well operation. A further'advantage is achieved by the method of myin vention in the fact that an increase in the hydrogen' l sulfideconcentr'ation of the gas cap, resulting as it does" in a-lowering of the retrograde condensation.pressure; wouldpermit if desired the rewc'le' of lower volumes'vof lean gas since greater reduction in pressure can be en-f countered in the 'formationiwithout causing n loss d" condensateliquids by retrograde condensation. With reference now to Fig. 3 an example will be described of a partially depleted crude oil reservoir wmch duction fromthe formation, well fluids dow from the well 70 `through line 71' and pressure reduction valve 72, and are introduced into separator 73 at a pressure below' reservoir pressure. Crude oil that has separated in the. n said separator is withdrawn-through line 74 tonaonvexr'l 'i tional means (not shown) for storing the oil. Gas ows liquid-separating means (not shown).

' through line 79 to an input well 80. v

Upon substantialdepletion vof the crude oil produc- I' tion, the formation is then in'pressnre by inec spades-e tion of gas through the input wellto a pressure in the retrograde condensation pressure range." This 'gas is en-- the order of the crit-ical of fluids and consequently includes such -'adus'nrentwl'uitlret-` riched-with hydrogen sulfide, which may'als'o have been added'with cycledgas during the voil production, so as to increase thehydrogen sulfide concentration of the formation, lower the retrograde condensation pressure,

and 'thus dissolve distillate hydrocarbons into-the major i phase and permit their recovery as gas condensate.

with the well uids. Hydrogen sulfideor gas containling hydrogen sulfide in a concentration higher than the' 'concentration of hydrogen sulfide inthecycled gas is introduced from a source 81 through valved line 82 into' or not the hydrogen sulfide content of the' iiuids is to' be raised or lowered by the adjustment. Thus lwhile rny preferredernbodiment of such a process of the.

said condensation pressure is the adjusting upwardly to: a predetermined amount of hydrogen sulfide time limits of abouti to 30 percent by volume, my invention'.

the recycled-gas line 79 and, in admixture with 'I cycled gas, through the input well S into the forma# tion. The addcdhydrogen sulfide 'can also be introduced into the gas line 76 ahead of the said compressor 77. The so introduced hydrogen sulfide-rich' gas mixture flows from the bottom 83 of the input well 80 into the formation and flows under the force of the higher injection pressure through the formation towards the well bottom- 84 of the production well 70 as indicated by arrows 85. The hydrogen sulfide-rich hydrogen gas includes also adiusunent downwardly fof the hydrogen.

suliide'gcontent for other luxrposes.` For example: the? well iluids from a gascondensate well'can 'be treated: v at pressures `above the retrograde-condensation pressurei "1- for removal of hydrogen sulde fromthc kfluids so that "I".

the, retrograde.' condensation Apressure will be -considerdably. increased. .Thereafter 'a substantial amount of liquid hydrocarbonscanbe recovered in a primaryseparator by retrograde condensation without lowering the 'i pressure of the well fluids to the degree formerly vaccessesY sary. Gas separated by this condensation step can be' l' scrubbed with absorbent oil at these high pressures andr the resulting gas can be returned to the formation withl i considerably less additional compression than 'wouldbeowing from the input well to the production well in the formation and will admix with the gas and oil in the formation and will form with the gas and liquid a gas phase of the retrograde condensation type..

The'higher concentration of hydrogen sulfide in the t cycled gas will also cause hydrogen suldeto dissolve f in liquid hydrocarbons in the formation thus reducing the viscosity of the oil and rendering'it more easily displaced by the cycled gases. It can be seen that' oil no vlonger recoverable by primary depletion' methods be vaporized and will pas with the well tiuids to the surface in 'the production well 70. i

'In an example of. operation according'to the inve ntion, a well fluid from acondensate type reservoir-'and containing 19 percent of hydrogen sulfide and 9 percent of carbon dioxide was produced. The formation tem`l perataure was 215`F. and the pressure was above its retrograde condensationpressure,A which was found to be 4450 pounds 'per square inch.4 The gas was then` passed .through a system for the removal of hydrogen. sulfide,v after which it was observed that the .retrograde required if it had been necessary to lower the pressuzte:`

of the fluids below the original retrograde condensation' 1.. method of producing vincreased yields of nor-.ijmally liquidhydrocarbons from a gas condensateWelk.`

which process comprises llowing well tiuids'oontaininx: hydrogen sulfide from aproductiouwell .toa zone ofv pressure reduced to below therctrograde condensation--l pressure of the well uids and thereby condensing liquid:X hydrocarbons from the fluids, withdrawing liquefied hy-'1.

drocarbons from the condensing zone, passing gascoultuids from thev condensing zone to a purification zone,"

separating acid gasesvincluding hydrogen .sulfide from the gaseous fluids in the purification zone, withdrawing hydrocarbon. gases substantially tree of acid gases from.

theV separation zone and compressing at least a .portion of 'said-gases, adding to the said compressed gases sui- Y cient' quantity of hydrogen :sulde of the said acid gasa.

to provide a hydrogen sulfide concentration of the com# pressed' gases higher than thatof the said well iluids and condensation pressure ofthe gas, substantially free' of hydrogen sulfide, had risen to 5370 pounds per square inch. The same well fluid, when its hydrogen sulde content had been adjusted to 9.78 percent, `exhibited. a

retrograde condensation pressure of 4975 pounds per square inch. In another example hydrogen sulfide was' added to. the well fluid to'provide a hydrogen sulfide concentration of v27.04 percent in which case the, retrograde condensation pressure was reduced to 4025 pounds per square inch.

As illustrated in Fig. 4,-increasing the concentration of hydrogen sulfide in a gas-condensate 'fluid eifects a linear reduction of the retrograde-condensation pressure.

Even small amounts of hydrogen sulfide', it can be seen, will reduce the retrograde condensation pressure in a typical condensate gas reservoir suflcicntly to substan- A tiallyprolong the operating period before such depletion phenomena as retrograde condensation occur. For ex. ample, addition of about live percent of hydrogen lsulfide to such a well uid will reduce the retrograde condensation pressure over 200' pounds per square inch'.

The amountof reduction in the retrograde condensation pressure which an individual well-fluid will show upon addition of a given amount of hydrogen sul'de'will i vary according to the original hydrogen sulfide contentf of the well fllui'ds.

gas ratio of the Well fluids appears to have considerably However', alternation ofthe oil to less effect on the retrogiadecondensation pressure or on the inuence'which-added hydrogen sulfide will vhave on the retrograde condensation pressure.

My invention comprehends the adjustment of the retro--y grade condensation pressure of petroleum uids at high recycling thev so-formed mixture of compressedgas -andhydrogen sulfide to the said weilformation.

2. A method of producing increased yields of normally liquid hydrocarbons from agas condensate'well, which process comprises flowing well lluidsy containing hydro gen sulfide from a production well to a zone of pres"v sure reduced to below the' retrograde condensation` pressure of the well lluidsand thereby condensng lq,

uid-'hydrocarbons from the tluids,. withdrawing lique-` gases to provide a hydrogen .sulfide concentration of the compressed gases at a selected concentration higher than that of the said well fluids and such that, when thecom- `pressed gases are added to fluids in the formation, a concentration of the formation fluids will rangebetwccn 1' and 30.volume percent, andrecycling the so-fo'rmed mix ture of compressed gas and hydrogen sulfide to the said `i well formation;

3. An improved method of operating a gas Awell tol produce an increased yield of distillate hydrocar.. bons, which method comprises: withdrawing uids a hydrogen sulfide content from the said well; separating distillate hydrocarbons therefromat a pressure less than the incipient-'retrograde condensation pressure of the wells uids; withdrawing soseparated gases and absorbing mid I. clean-gas derived at least in part as a fraction .o

. duced crude oil and hydrogen sulfide .in admixture with maintaining the hydrogen-sulfide content' of 7 gases in a liquid absorbent; strippingacid gases from the srv-enriched absorbent; scrubbing gases from. which acid gases have been removed with va. hydrocarbon carrbons have been removed to a pressure in excess of the 8 gaseous phase, which method'vcotupriaes-I' t the said formation a gas after saidintroducton of gas containinghyhlsnlde ahrbent to recover liquid hydrocarbons therefrom; com- 'pressing ga's'from which the acid gam and liquid hydrosaid formation pressure; mixing with the .so-compressed' i a'n'd gases containing hydrogen sulfide and additional;

hydrogen-sulde-containing gases from an outside source; introducing the compressed gas mixture into the formationfthe said hydrogen sultid'e'of the lean gases and that hydrogen sulfide obtained from an outside-source being addedto the formation in an amount that will increase the hydrogen-.snide content of uids. in the said formation; and withdrawing fluids from the formation having an ini, creased hydrogen-sulfide content. 4t A. method of operating a depleted crude oil well torecover ,additional quantities of. liquid hydrocarbons.

, therefrom, which methodcomprises: introducing into a partially depleted formation underlying said oil well dur'-v ing production of crude' oil, the' uids in the formationsupplying the crude oil containing some hydrogen-sulfide,

the lean the lean gas mixture-at a concentration in excess of the hydrogen-sulfide concentration of uids in the formation;

continuing production of the crude oil until primary recover-y is completed; subsequently operating said we ll as a: gas condensate well, the. pressure within the formation recovery in the'well tluidx.

1in :he said formation, and thereby pm .I

introducing another gas 'having a substnnudyherco'ncentrationtof hydrogen sulfide, the said- -f e1 hydrogen'sultk in each oase beingfso seiee'liunpal ultimate difusion of hydrogen sulde heb the resulting average concentration of ill. the uids'of lhefmfmatiowll be between l dador 30 volume p'ercem, and thereby reducingy the condensation-pressure of the well uids abruptly in incrcrnents so as ,to reabsorb liquid hydrocarbon, whieh have condensed out of gaseous phase during of the well, into the 4gaseous phase and retain in the gaseous phase in theI formation and punit tharj 7. An improved method of operating; gas

well that'produces uids from a formation unix-apres Y sure in the order of the retrograde connnge d'- the well` uds, which method comprises: ing inw the said formation 'a gas containing hydrogen mlde in higherconcentration than the concentration of hydrogen sulfide foundV to be present in the produced wel #nids to increase the hydrogen suld'e. concentration d im fluids' ducing the retrograde condensation pressure d te welltiuidssoas to retain hydrocarbons in gaseous-Haase in the formation Aand permit their recovery in the el uids beingmaintained in excess of the retrograde condensation pressure of finids in the formation by the said introduction of lean gas and hydrogen suliide into the formation maintaining the lhydrogen-sulfide concentration in the' formation in excess of the hydrogen-sulfide concentration originally occurring therein, and thereby reducing the retrograde condensation pressure 'of the uids in the formation to avalue below vthe pressuremaintained in the forma-- tion during gas condensate welloperation.

A5. The method ofclaim 4 wherein lean gas and hydrogen suliide'frorn an outside source are also pumped into.'

the` well formation to reduce the rate of decrease in pressequent distilate hydrocarbon production and to mai'nthe hydrogen-sulfide' concentration in the formation4 :sure irl-the. well during crude oil production 4.and

at'a value .in exoessof the concentration originally exist-V ing in the formation;

6L An improved method'of operating oill and gas WellsV that produce petroleum uids from a formation under a pressure in the orderof the retrograde .condensation range of theweil uids and'ofa magnitude that the uids are in;

8. An improved method of operating a gas codenaamwell that producesuds from. a formation under a prY sure in the retrograde condensation range of & well-- fluids mixture, which method comprises intrrinto theformation a gas containing hydrogen sul: in mdr concentration that when it mixes with Well his in the .formation a concentration of hydrogen sulfide d Ine well tluids will range between 1 and 30 percent byl'me'nnd thereby proportionately reducing theretrt'sgr'aclecandeur.-` tion pressure of the well iiuids so.as to retain kunneni bons in gaseousphase -in the formation and per-'t theirv recoveryinthewelluidn 1135,319 2,358,920 GRIISO!! N, 194I Nelly --.awa-.ew In. 8, 1952 

1. A METHOD OF PRODUCING INCREASED YIELDS OF NORMALLY LIQUID HYDROCARBONS FROM A GAS CONDENSATE WELL, WHICH PROCESS COMPRISES FLOWING WELL FLUIDS CONTAINING HYDROGEN SULFIDE FROM A PRODUCTION WELL TO A ZONE OF PRESSURE REDUCED TO BELOW THE RETROGRADE CONDENSATION PRESSURE OF THE WELL FLUIDS AND THEREBY CONDENSING LIQUID HYDROCARBONS FROM THE FLUIDS, WITHDRAWING LIQUEFIED HYDROCARBONS FROM THE CONDENSING ZONE, PASSING GASEOUS FLUIDS FROM THE CONDENSING ZONE TO A PURIFICATION ZONE SEPARATING ACID GASES INCLUDING HYDROGEN SULFIDE FROM THE GASEOUS FLUIDS IN THE PURIFICATION ZONE, WITHDRAWING HYDROCARBON GASES SUBSTANTIALLY FREE OF ACID GASES FROM THE SEPARATION ZONE AND COMPRESSING AT LEAST OF PORTION OF SAID GASES, ADDING TO THE SAID COMPRESSED GASES SUFFICIENT QUANTITY OF HYDROGEN SULFIDE OF THE SAID ACID GASES TO PROVIDE A HYDROGEN SULFIDE CONCENTRATION OF THE COMPRESSED GASES HIGHER THAN THAT OF THE SAID WELL FLUIDS AND RECYCLING THE SO-FORMED MIXTURE OF COMPRESSED GAS AND HYDROGEN SULFIDE TO THE SAID WELL FORMATION. 